1. Field of the Invention
The present invention relates to a shaft, in particular a drive shaft for a wind turbine power generator, and a wind turbine using such a shaft.
2. Description of Related Art
Rotor support-type wind turbines are a known alternative wind turbine design, wherein the structural load of the hub and rotor blades is provided by a fixed support shaft provided on the wind turbine main frame. As the hub is allowed to rotate freely about the support shaft, consequentially the structural load is transferred to the main frame while the torque provided by the spinning rotor blades is transferred to the generation system.
U.S. Pat. No. 4,757,211 disclose a rotor support-type wind turbine wherein a rotor hub is mounted onto a cylindrical section of the machine housing, the structural load of the rotor hub being supported by the machine housing. A hub shaft extends from the hub to the gearbox, and is accordingly coupled to the generator. Such a shaft is a typical, stiff-bodied drive shaft.
One of the disadvantages of such a system is that in order to compensate for vibrations and bending moments transferred through the hub shaft from the hub, the generator and the gearbox must be mounted on vibration damping elements which are coupled to the machine housing. Furthermore, the hub is mounted to the machine housing utilizing flexible bushings and further damping elements. Damping elements can also used in such constructions to compensate for misalignments between turbine components, e.g., in the case of the hub shaft and the gearbox not being perfectly aligned.
Such damping elements are subject to wear and tear during the lifetime of the system, often requiring replacement every 3-5 years in a relatively costly maintenance operation, at which time the turbine must be taken out of service for an extended period of time.